The transformation of biomass into fuels and chemicals has received intense global attention in the past decade due to growing concerns over diminishing reserves and volatility in the petroleum market, alongside the environmental impact of releasing vast tonnages of legacy carbon into the atmosphere. The geographic preponderance, renewable nature, and low cost of plant biomass, particularly waste biomass, makes it an ideal resource for sustainable generation of products that would otherwise be derived from petroleum.
Of the approaches to biomass processing that have advanced into commercial practice (microbial, pyrolytic, and chemical-catalytic), a major advantage of the latter is that, in some instances at least, the native structure of the carbohydrate is preserved in the form of the furan ring. Historically, in no case has this been more notable than in the production of 5-(hydroxymethyl)furfural (HMF) 1 from fructose. See, for example, reviews by van Putten and others (e.g., Chem. Rev. 2013, 113, 1499). HMF has been cited as a platform molecule of exceptional promise, with multiple applications to polymer, fine chemical, and fuels production. However, the preparation of HMF from sugars other than fructose or from cellulosic sources is complicated by low yields and difficult isolation from aqueous reaction media. As noted in the above-cited review, significant challenges still remain in transitioning HMF production to an industrial scale. No HMF pilot study has successfully employed raw biomass, and although a small number have been operated using sugar feedstocks, this practice is not expected to be economically competitive in the long run.

A solution to the above problem has been proposed in the form of 5-(chloromethyl)furfural (CMF) 2, a stable, hydrophobic analogue of HMF which presents no isolation issues in its production. CMF is prepared under mild conditions and in high yields from sugars, cellulose, or directly from cellulosic biomass by treatment with hydrochloric acid in a biphasic reaction. See, M. Mascal, E. B. Nikitin, Angew. Chem., Int. Ed., 2008, 47, 7924; and M. Mascal, E. B. Nikitin, ChemSusChem 2009, 2, 859. While it might be supposed that the requirement for strong acid in this process is disadvantageous, it should be noted that the use of HCl in the chemical industry is long established, and numerous reactor materials have been developed to accommodate it. Multiple technologies for its recovery from solution are also available, including membrane distillation, pervaporation, evaporation, acid base-couple extraction, solvent extraction, diffusion dialysis, and electrodialysis.
The preservation of the furan ring system in 1 and 2 gives access to useful derivative chemistries that other chemical-catalytic routes forfeit, for example those that generate levulinic acid directly from biomass. One of the most sought-after furanics of recent times has been 2,5-dimethylfuran (DMF) 3, and several recent publications have been devoted to its production from HMF 1. In addition to being a high energy density, high octane biofuel, DMF 3 can be converted into p-xylene, a high-volume chemical intermediate used for the production of terephthalate polymers. The potential of 3 to unlock key renewable markets is thus vast.
High yields of DMF 3 from the reduction of HMF 1 have been previously reported. HMF has been hydrogenated using a novel Ru/Co3O4 catalyst to give DMF in 93% yield, while a bimetallic nickel-tungsten carbide catalyst has been used to provide DMF in 96% yield. PtCo nanoparticles and Ru/C catalysts have afforded DMF in 98% and 95% yields, respectively. However, whether or not these methods are themselves industrially practicable is not so much the point as the fact that they all start from HMF. In effect, no technology is any more scalable than the practical accessibility of its feedstock. Straightforward, industrially viable methods for the production of dialkylfuran products such as DMF are needed. The present invention addresses this and related needs.